Horses and other hoofed animals are susceptible to numerous injuries and ailments associated with defects in their hooves. Cracked hooves, for example, are a common occurrence in horses and can render an animal unserviceable for extended periods of time, typically 6 months to a year for medium or large sized cracks, until the entire hoof has had sufficient time to regrow.
The horse hoof is a non-vascular cornified epidermis of the animal's foot consisting of a wall, a sole and a frog. The wall is made from keratinized epithelial cells which overlay a sensitive lamellar corium tissue containing water in addition to numerous minerals. The ground surface of the hoof can be divided into three zones: the toe zone, the quarter zone, and the heel zone, all of which are susceptible to cracking.
Horse hoof cracks can be caused by essentially anything that impairs the elasticity of the hoof, weakens it, or causes overloading. The most frequent causes of hoof cracks include physical impact/trauma, poor hoof and leg conformation, imbalance of the hoof, improper trimming or shoeing, and invasion of the white-line by bacteria, fungus or mold. Genetic predisposition, nutritional imbalances, dry or brittle hooves, or those having excessively thin walls, can represent predisposing factors to hoof cracking. Once a crack occurs, the hoof wall often pinches and irritates the underlying laminae within the hoof capsule due to the expansion and contraction of the hoof during loading and unloading. Lameness and/or extended unserviceability is an unfortunate and costly consequence of many cracked hooves.
Various approaches have been used to minimize the difficulties associated with hoof cracks. Typically, treatment involves an attempt to remove pressure from the free extremity of the crack and immobilize its edges. Conventional methods for repair include proper balancing of the hoof, corrective shoeing, grooving of the hoof wall, use of clamping across the crack with nails, a Vachette clamp, or mechanical clamps, and use of various prosthetic hoof repair materials such as acrylic, fiberglass, or epoxy resins in combination with umbilical tape or wire, sheet metal screws, or other synthetic materials. (See for example, Nickels, F. A., "Hoof Cracks", In: Current Therapy in Equine Medicine, vol. 2, Robinson, N. E. (ed.), W. B. Saunders, Phil, Pa. (pub.), 1997)
Lacking from the prior art, however, are effective biologically-based approaches for treating hoof injuries. Methods for accelerating the rate of hoof growth would be desirable because they could significantly reduce the length of time required for an animal to recover from a cracked or otherwise injured hoof.
Somatotropins, also known as growth hormones, are polypeptides produced and secreted by cells of the pituitary gland. These proteins, which can be produced reliably and inexpensively in large quantities by recombinant DNA technology, are known to be effective in promoting pre-adult skeletal growth and meat production of beef cattle and swine. In addition, they are known to affect a variety of metabolic processes including the stimulation of lactation, improvements of the efficiency of converting feed to meat or milk, and lipid-mobilizing effects.